Vapor electric apparatus.



G. A. KRAUS & R. D. MAILBY. VAPOR ELECTRIC APPARATUS. I

APBLIUATION FILED JUNE so, 1910.

Patented Dec. 3, 1912.

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uNrrED .sri-atrasA @TENT OFFICE CHARLES A. KRAUS, OF 'NEWTON HIGHLANDS,AND ROY D. MAILEY, 0F LYNN,

MASSACHUSETTS.

VAPOR ELECTRIC APPARATUS.

Specification of Letters Patent.

Patented Dec. 3, 1912.

Application led June 30, l1910. `Serial No. 569,693;

' and ROY D. MAILEY, both citizens of the United States, and reside-nts,respectively,

of Newton Highlands and Lynn, in the counties of Middlesex and Essex andState of Massachusetts, have invented new and useful Improvements inVapor Electric Apparatus, of which the following is a specification.

Our invent-ion relates to the construction of vapor electric apparatusand has for its object the provision of an electrode structure whichwill be durable, as little as possible susceptible to breakage and whichin its electrical operation shall po-ssess large capacity, eiiiciencyand ability to preserve continuity of operative conditions.

As a typical example of vapor electric apparatus we take for purposes ofdescription a vapor rectifier of which the characteristic members are ahermetically sealed container to include highly rarefied' mercury vapor,at least two anodes and one cathode and leads from these electrodeswhich pass through the walls of the container.

Vapor rectiiers such as heretofore generally used have employed glass asthe material of which the container is composed. Owing to the diiiicultyof sealing leads of generous dimensions through the walls of a glasscontainer, and owing also to the diiiculty of withdrawing heat fromdiffer-V ent parts in the interior of the container, it has not, so faras we are informed, been found feasible to construct( durablerectifie-rs capable of converting currentsl substantially in excessof'50 amperes. Glass rectiiers even of this capacity aredisadvantageously large considering the nature of the material of whichthey are composed and thus present difficulties in manufacture, whilebreakage in handling, and transportation of such glass rectifiers hasproved a serious source of loss. Moreover, a glass container and rectierwhatever its size, is by its i nature and under the conditions ofoperation a delicate apparatus since its interior `is exhausted to verylow pressure and contains a body of liquid mercury which under thevacuum conditions is liable to break the container unless it is handledvery carefully.

It has been suggested to employ metal as the material for containers ofsuch apparatus, but so far as our experience and observation go, thedesign and structural featuresof such apparatus have not been so farperfected as to afford a vapor electric apparatus which meets theconditions 'of commercial requirements. A difficulty has been in thelack of known means for introducing the electrode leads through thewalls of the container in such amanner as to provide forelectricalinsulation, impervious as to gases and resistance to'thermal change andmechanical shock. 7e have invented a new -mode of unit-ing electrodeleads to a metal container which will be herein shown and described butwhich forms the subject matter of an application for patent of theUnited States Serial No. 514,908, tiled by us on or about the 27 th dayof August, 1909.

In a rectifier capable of converting 1000 amperes', presumably 15,000oules of` energy are expended per second within the container, of whichabout one-third is developed at the anode surfaces. To be eective, anapparatus to accomplish such a conversion must be provided not alonewith means for withdrawing heat through the walls of the containeritself, but also with means for disposing of the heat generated at theelectrodes. For a given resistance the amount of heat evolved in theelectrode leads themselves is proportionate to the square of thecurrent. At 1000 amperes the heat developed would be thus 400 timesasfgreat as in a rectifier carrying only 50 amperes. Therefore, in arectifylng apparatus which is to carry large currents it is necessary tomakethe electrodes and their leads of very substantial dimensions andthis necessity further increases the ditliculty of providing' insulatingjoints between the leads and the container which are capable ofwithstanding the mechanical and thermal strain placed uponl them. Thesedifficulties, however, while very largely met and compensated for by theimproved joint referred to in our said application Serial No. 514,908,may still further be obviated by the employmentof means for regulatingand dispersing the heat incident to the operation of such an apparatus.

The accompanying drawing illustrates an example of vapor electricapparatus embodying the within described inventions. This drawingrepresents in vertical section, a mercury arc rectifier of which A is ametal container preferably cylindrical in form and lconstructed of coldrolled steel. The sides, top and bottom of this container should be asthin as is consistent with the requisite. strength so that the weight ofthe rectifier' may be reduced to a mimimum and its heat radiatingcapacity be as large as possible.

B and C are the anodes; B', C ,their respective leads; D is a mercurycathode insulated from the container by an enamel lining E; and D is thecathode lead which, like the anode leads, is introduced through the topT of the container.

The leads are attached to and insulated from the container by the jointsconsisting essentially of two steel tubular members G and H to which anannular member of vitreous or fritted insulating material F fused bymeans of a suitably low-mclting vitreous flux.' The tubular members Gare Welded to the top T of the container and therefore constituteextensions of the container wall. The outer ends of the tubular membersH are welded respectively to the electrode leads B, C', D. The tubularhoods Acomposed ofthe metal members G and I-I and the insulating annulusF thus surround the leads which, in4 passing through the extensions, arespaced from the innelkwalls thereof so that the joint itself is notheated by direct contact with the lead of which the temperature may beconsiderably elevated.. Since a vacuum intervenes between the lead andthe internal Walls of the hood which comprises the joint, it is only byradiation that heat may be transferred across. The junction between thelead and the outerI tubular member H is made at some distance above thefused joints, so that the heat conducted through the metal hood member His reduced as far as necessary; electrode connections and joints such asabove described constitute the subject matter of our said applicationNo. 514,908.

The rectifier herein illust-rated is shown as, provided with one mainanode E and a smaller auxiliary anode C. A complete single phaserectifying system would consist of tWo rectifying units of the typeherein illustrated which may be connected according t-o the systemdescribed in application for United States patent Serial No. 514,907,filed on or about AugustQ?, 1909. In such system the anode C is merelyan auxiliary anode of -which the purpose is to maintain the arc duringthe half cycle when thefarc is inoperative at the main anode. While ourimprovements herein described are not restricted to use with rectifiersof this special type,` they are so shown since We find this typeparticularly useful in the rectification of `large currents. Another'advantage inheres in the fact that the current flowing in the rectifieris small at the time the potential between the cathode and the anode isat a maximum. In a 500 anipere rectifier working at l1000 volts(virtual) the auxiliary current may be made as low as three amperes. Ifthe customary type of rectifier is employed wherein both anodes do equalduty, the current atthe active anode would be 700 amperes at the timethe potent-ial'at t-he other anode is at its maximum value, say 1400volts. The presence of a high current on vone electrode i u a rectifierwhile the potential at the other electrode is high, We have found to beconducive to the breaking down of the surface resistance to the passageof the current through the inactive electrode; in other words, underthese conditions the electrode is liable to lose its effectiveness as anelectrical check valve so that an arc is formed between the anodes ofthe rectifier, interrupt-ing the normal operation of the apparatus andexposing it to danger of injury. Therefore, We recommend that only asingle main anode be included in a container. Under these conditions itis possible to place the anode directly above the mercury and in closeproximity thereto, an arrangement which insures greater flexibility andcertainty of operative conditions and also reduces to a minimum t-h`epotential drop between the anode and the cathode since this potential isa function of the distance between t-he anode and the cathode.

As we have already pointed out, in current rectifiers of large capacitya large amount of heat is necessarily generated at t-he surface of ananode. The temperature of an anode should not be allowed to reachv toohigh a value because this is liable to produce an evolution of gases'which are 105 undesirable in a rectifier and is also liable to impairthe check valve efficiency of the electrode. The temperature of theanode depends upon the quantity of energy dissipated at .itselectrically operative surface and on t-he area of its radiatingsurface.

If the anode is placed fairly near the mercury surface of the cathodethe greater portion of the current passes through the portion of theanode lying nearest the cathode and as a result such portions of theanode are raised to a much higher temperature than others. In general,it will be found necessary to make the radiat-ing surface of the anodemuch larger than the active electrode surface. It is highly advantageousalso to provide for ready conduction of heat away from the activeelectrode surface toV other portions of the apparatus which may act asradiating surfaces. As metals of .high radiating capacity, such ascopperl or silver, would be attacked and eventually dissolved bymercury, it is not practical to employ them in situations where theycome in Contact with metallic mercury or mercury vapor. We have,therefore, constructed an anode with a core of copper enveloped in upperportion at the sides and top of this electrode marked WV, acts merely asa radiating surface and heat is conducted to thls surface by the coppercore J. If desired,

the surface W may be treated so as to improve its radiating capacity; itmay be oxidized superficially or given ablack coating for this purpose.(The above described electrode structure, involving a highly conductivecore, protected by a shell of material unaffected by mercury, forms thesubject mat-ter of an application for patent, Serial No. 569,695, filedby us on or about June 30, 1910.)

The characteristic check valve action. of a rectifier-,anode dependsupon its physlcal condition as a non-volatile solid material. lf,therefore, liquid mercury strikes the anode the valve action is liableto be interrupted by the presence of a volatile material y upon it andthis volatile material, if present on the anode, usually causes theformation of a cathode are. When a rectifier is in operation the mercuryof which the cathode is composed is in more or less violent agitationand particles of it are constantly being spattered and thrown off andtherefore when, as we prefer for reasons stated above, the main anode isplaced near to the cathode surface, it is advisable and, in many cases,necessary to screen the anode against the approach and contact of liquidmercury. For this purpose we surround the sides of the anode and theanode lead by av shield or jacket M of insulating material such asglass, porcelain or fused quartz and secure thereto at the lower end ascreen N which may be composed of iron-wire gauze, or a perforated plateor plates; the essential characteristic of such screen being that itshall be pervious to gases and afford a path for the current through thegas, while serving as a protection herein against the passageof liquidmercury particles.

Not only does the screen N protect the anode B from being spattered withliquid mercury, but also with an arrangement such as just described, thevapor in vigorous circulation from the cathode does not pass immediatelyby and over the anode surface. ve find this to be advantageous sincewhen large currents are being rectified, the mercury vapor circulateswithsuch speed and violence as to carry particles' of liquid mercuryalong with it and cause them to impinge upon the anode surface. If, asis sometimes the case, it is desirable t allow a gentler stream ofmercury vapor to pass overthe anode surface in order to remove foreignygases therefrom, this controlled and beneicial circulation may besecured by providing small openings as m in the upper part of the hood Mwhich surrounds but does not hug closely to the sides of the anode B.Vith this arrangement, even though the mercury vapor currents in themain body of the container are violent, the screen N and Ventilatingopenings m regulate and modify the gaseous currents so that the benefitof washing vthe anode with mercury vapor may be secured withoutincurring danger from spattering of liquid mercury.

In order to provide an electrode of which the electrically activesurface shall be of small extent in contrast with the heat radiatingsurface, we make the electrode preferably in the form shown in thedrawings, namely, an inverted cup or bowl on which the electricallyactive portion will be located for the most part, if not entirely, uponthe rim K, the remainder of the surface of this electrode affording acomparatively large heat radiating area. While some heat radiation willproceed from the interior of the cup or bowl, the chief advantage inmaking the electrode thus bowl-shaped lies in the reduction of its totalweight, excess weight being disadvantageous for the reason that thewelded and fused joints by which the electrode lead is secured to thecontainer are necessarily of small area and relatively distant from theactive electrodeitself; hence an excessively heavy electrode at the endof the long electrode lead will endanger the integrity and permanency ofthe sealing joints. The function of the electrode core J is thermalonly, as it is assumed that the steel or iron of which the lead B iscomposed possesses ample current-carrying capacity. Thus, the core Jneed not extend l into the lead B', as its function is to conduct heataway from the active anode surfaces which are presented to the cathodeand are relatively small, to electrically inactive parts of thestructure, whence heat will be radiated. So long as the outer metalshell of the electrode and its lead suiiice to carry current, the coremight be. electrically nonconductive, if there were such a thing as arood thermal conductor which is also elec- 2tjrically non-conductive.

s That we claim and desire to secure by Letters Patent is:

1. In a vapor electric apparatus, a container including a mercurycathode, an electrode suspended within the container and a shield ofinsulating'material surrounding trode suspended 4Within the container, a

shield of insulating material surrounding said electrode provided witha'screen pervious to mercury vapor -between said electrode and themercury cathode.

3. ln a vapor electrlc apparatus, a container including a mercurycathode, an elec- -trode suspended within the container, a

shield of insulating material surrounding sald electrode provided W1th ascreen ervious to mercury vapor between sald e ectrode and the mercurycathode, and with Ventilating apertures to permit circulation of Vaporwithin the shield over the electrode surface.

4. In a vapor electric apparatus, a container containing a mercurycathode, am electrode suspended within the container and a shieldcomprising insulatingvmaterial surrounding the electrode, and a screenbetween said electrode and mercury cathode.

Signed by us at Boston, Massachusetts, this twentieth day of June, 1910.

CHARLESA. KRAUS. ROY D. MAILEY.

